Ceramic/metallic composites as a novel material which show a combined nature of ceramic and metal are useful for application to construction materials or the like. For manufacture, a technique called SHS is known, which is based on the process which occurs with a certain material system: a combustion, once initiated by igniting at a spot, sustains itself and propagates throughout the rest of the material, due to an intense production of heat which spreads and causes a sufficient temperature rise. This technique advantageously facilitates the preparation of a substance of melting point over 2000.degree. C., and useful for the production of functional materials such as carbide, nitride, boride, silicide or oxide of the fourth or fifth group metals of the periodic table, including Ti, Zr, Ta, Si, as well as intermetallic compounds. The technique is fully described in "The chemistry of SHS", published by T.I.C. (1992).
It is known that the synthesis process can be initiated by:
(1) putting into contact with an electroresistive heater or like a pellet, or formed compact body, of mixed powder so composed as to be capable of SHS (direct ignition) and igniting at an end;
(2) providing, in contact with the pellet at an end, another mixed powder of SHS capable composition; the latter is ignited and the resulting intense heat is used to ignite, in turn, the pellet (two-step ignition); and
(3) heating with a heat source (electroresistive element, for example), which is provided around, so as to ignite the formed compact body (indirect ignition). Of the three above, the techniques (2) and (3) are commonly employed for the purpose of facilitating ignition to the pellet body when the principal heat source is insufficient for the self-propagation of the process: it uses as a secondary heat source a premixed powder which is provided around the compact body as described above.
Thick or massive composites can be obtained by an SHS-based sintering technique when the SHS products either melt or soften. However it is hardly the case with titanium carbide composite, for example, which is obtained as a porous product, when prepared with a starting mixed powder of metal and carbon. Probable reasons are: (1) the carbide product has a melting point too high, and (2) a solid state reaction can take place between Ti and C at rather a low temperature, and produces TiC which forms a firm network. Here densification may be achieved to a degree by compression, but it is impossible to obtain a product substantial free of pores. This is also the case with the synthesis of other high melting materials.
An SHS process, which can produce high temperatures over a short period of time almost adiabatically, is employed for the formation and sintering, simultaneous or subsequent, of high melting materials and, if tentatively, for the preparation of compact of various materials. For the materials, these techniques are available: static compression with a mechanical press, instantaneous compression by explosive detonation, isostatic compression with a HIP system, pseudo-HIP process whereby the formed compact is squeezed from around with a mechanical press in a die by means of molding sand.
On the other hand, composites of diamond or high pressure polymorphism of boron nitride (cBN or wBN), either interjoined or dispersed and held in the matrix, are widely employed in industries. The superabrasive substances are metastable under normal pressure and more so at high temperatures such as used in the sintering process: they both can transform rapidly to the low pressure polymorphism, that is graphite or hexagonal boron nitride, so an ultrahigh pressure is needed in order to prevent such unfavorable transition processes by establishing a condition where those superabrasive substances are thermodynamically favored phases, and pressures of several (more than four, commonly) gigapascals are exerted in sintering processes. Thus the volume available poses limitation to the largest product dimensions achievable, which is currently around three inches (76.2 mm) in diameter.
Some less firm-structured wear-resistant materials wherein super abrasive particles are not necessarily interjoined, are tentatively prepared by means of either HIP or hot pressing, instead of the ultrahigh pressure technique. These processes are advantageous in that larger wear-resistant products can be achieved as essentially free of equipment related limitation, while in the manufacture of heat resistant composite products a maintained temperature of 1000.degree. C. or more is needed for several minutes for the densification of the matrix, due to the nature of the process and implementation. This inevitably causes transition, partly or essentially, of the superabrasive to the low pressure phase, and resulting deterioration in particle properties and retention to the matrix make it difficult for these wear-resistant materials to be substituted for those ultrahigh pressure compacts.
SHS processes cause often a temperature rise to more than 2000.degree. C., although heat evolves usually over a short period of several seconds. No techniques have been available, as far as the Inventors are aware, which could apply such almost instantaneous heating to apply in the manufacture of compacts, of composite or not, which comprise superabrasive particles.
Therefore, one of the principal objects of the present invention is to provide an effectively densified compact body of titanium carbide and other ceramics which are difficult, as described above, to be produced as a dense compact by SHS, and in particular, such construction material which consists of a ceramic skeletal structure, densified with metallic phase which is filled in the internal gaps by penetrating with fused Ti--Al alloy (or intermetallic compound). Another object of the invention is to provide an adequate method for the preparation of such compacts.
Another object is to provide a novel superabrasive containing compact which is essentially free of heretofore inevitable llimitation in the product size and deterioration in abrasive strength. A further object is to provide an effective method of producing such compacts.